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In a message dated 8/4/01 7:39:52 PM Eastern Daylight Time, joe@po*.co* writes: > How could a fin with less surface area and rigidity possibly generate more > thrust in the water than a fin with greater surface area and rigidity? > > People like them because they are easy to kick with. But you travel less > distance. Personally, I'd rather kick hard once to cover a given distance > than kick easy three times. > > The manufacturers simply had nothing to sell so they made this up. Funny > how people that buy this kind of stuff typically keep going back to the > stuff in their garage that works. > > Joe =================================== Amen Joe ! I met the guy who developed these on a dive boat while they were still in the prototype stage. We both wanted to see how they would perform for a diver pushing doubles (which I happened to be using), so he took my video camera and I put the fins on and we kicked around a shallow reef for a while (second recreational dive). He also had a handheld speedometer that allowed me to read my speed as I switched between my own fins and his new design. It took a while for me to get the hang of the kick and we surfaced occasionally for instructions and lessons. Now and then I would get the kick right for a while and the speed I could attain was, indeed, a tad better than with my own fins but I was having to work leg muscles a lot harder to do it - not only to kick faster but to move the fin through the water at the correct angle of attack. His theory was that they were more aerodynamic because they imitate the action of a wing and because they reduced turbulence behind the fin and, therefore, provided more forward thrust; BUT to take advantage of this greater thrust you had to kick differently in order to bend the blades into the right angle of attack with the water relative to your direction of travel. You also had to kick faster. Consider that kicking a pair of fins requires that you move the mass of your legs back and forth breaking the inertia of that mass every time you change direction of the leg's movement. If you have to kick faster to make any fin work comparably to another this factor adds WORK to the formula. Work = gas consumption = CO2 buildup = inefficiency because it is work you have to do just to keep the fin in the proper shape and position rather than to propel you forward. Though my top speed was a tad lower with my own stiff fins I was doing much less work. It does not matter how efficient these "could" be if the work of moving the mass of the legs more often and of using additional muscles to keep the angle of attack correct (change the way you kick) adds more work than you gain by the design. These fins are a marketing gimmick in a market desperate for something new ! The only advantage I can see in them is that they might reduce ankle fatigue for snorkelers where power transfer to the water is a minor concern (Possible reduced twist of the fin). I have not seen these advertised as a good choice for technical diving so I do not see anything sinister about their sales pitch, and if they make it more fun for recreational divers to use them then more power to them. For cave and most other technical diving you want a fin that will allow you to move backward or forward a little with just a movement of the ankle - stiff ! How many of you with these fins were taught how to kick with them to make them work properly when you bought them ? The guy who designed them stressed constantly how important this was during my trial run. Chuck Boone -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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